Arch dam



March 1953 u. FINSTERWALDER 2,631,434

' ARCH DAM Filed May 29, 1950 i 9 i I I I L. 2 JT MWV/ FL-MMETWW A WI $74 5 $320,,

Patented Mar. 17, 1953 ARCH DAM Ulrich Finsterwalder, Munich, Germany Application May 29, 1950, Serial No. 164,962 In Germany October 1, 1948 2 Claims. 1

This invention relates to an arch retaining dam. In the construction of barrages or dams across a valley, there have been used for some time dams in which the pressure of the water is resisted by a solid structure shaped according to the laws of hydrostatlcs and generally of a substantially triangular cross section. Such structuresin general are termed gravity dams.

In recent times it has been found very difficult, more particularly in cases where the dams are high, to prevent the formation of cracks. Such cracks in general are caused by stresses set up in the structure as a result of the temperature rises occurring as the concrete is setting, and of the decrease of temperature in the subsequent cooling process. The cracks thus occurring neutralise the uniform wall effect and reduce the safety of the structure in a dangerous degree.

Therefore, in the past there has been adopted a design of dam in which the triangular cross section of the dam is retained but made more slender, and in which, moreover, the dam, as viewed in plan, was not made straight, but designed in a curved form. Such dams are known as arched gravity dams. V

The known retaining dams of this type generally can be given only a relatively slight curvature, since the so-called cap of the dam or wall is generally of great length. In arched gravity dams with a slight curvature the main water pressure is transmitted tothe ground at the base of the dam, only a small part being transmitted to the sides by the arch action.

In so-called arch dams the forces resulting from the arch formation are transmitted directly to the sides of the barrage, producing in the dam a pressure which helps to close any cracks that may be formed in the dam. From the standpoint of safety the design of a retaining dam in the form of a pure arch dam would be preferable to a design in the form of a gravity dam. The amount of material required is also substantially less in an arched dam than in a gravity dam. However, in practice a pure arch dam can be used only when the natural conditions of the ground are very favourable, i. e., where the sides of the valley are steep, so that the crest of the dam will become relatively short. Such favourable conditions of the ground, however, are very rare in practice.

Furthermore, there are known designs of dams in which the solid block of the gravity dam is broken up by recesses into a number of buttresses with a plane or arched portion extending in front of these buttresses. Such a dam is referred to as a buttressed dam.

In such dams in a static respect the principle adopted is similar to that in gravity dams. Owing to the reduced dead weight of buttressed dams it is necessary to increasethe width of Z the foundation base in order that the resultant of water pressure and load will have a point of application within the foundation base.

The objections to be raised against said gravity dams in regard to the safety of the structure would apply to buttressed dams as well. Admittedly, in buttressed dams there is the advantage that cracks formed in the buttresses and becoming dangerous can be seen whereas, since cracks in a weight dam form in the interior of the structure, they cannot be seen from the outside.

It is an object of the present invention to provide means which render it possible to utilise the working principles of an arch darn where the normal application of this principle, considering the conditions of the ground, i. e., the required length of the crest of the dam, so far was regarded as uneconomic.

With thisobject in view, according to the present invention the dam which is an arch dam with abutments in the form of buttresses and with secondary retaining walls arranged between the said abutments and the sides of the valley is designed as an arched gravity dam, and the said abutments are supported on a rising foundation base arranged in the side of the valley. Thus, the radius of the dam which is formed with a circular arch, viewed in plan, can be easily kept so small that a very substantial part of the horizontal thrust of the water is transmitted to the sides of the valley by an arch effect, thus reducing the thrust on the ground at the base of the dam accordingly. Therefore, the weight of the dam is sufiicient to transmit the remaining thrust safely to the bottom of the valley. Thus, by the present invention the disadvantages existing with pure arch dams are avoided, but on the other hand the advantages of the gravity dam are utilised. In the lower part of the dam the arch in each case has its abutment at thesides while in the upper part this will be the case only where the conditions of the ground are very favourable. This, however, will almost never occur with dams of a considerable extent. However, by supporting the abu-tments on a rising foundation base embedded in the sides of the valley, the advantages arising from the use of an arch will be realised even with unfavourable conditions of the ground.

According to a further feature of the invention the main dam or wall is given a constant wall thickness throughout its length and provided with a foot-like enlargement at its downstream side in continuation of the foundation base.

It is also contemplated to give the main wall above the foundation base a double-curved preliminary arch directed towards the water side, which arch is seated on the foundation base with an inclination towards the downstream side of the wall.

Owing to the dead weight of the wall there is produced in the zones above the foundation base a downwardly directed force which balances the water pressure, while the horizontal force is neutralised and radial deformations producing-bending stress are avoided. In the upper zones in which the radius of curvature becomes zero or is transformed into a reverse curvature, the horizontal component is not changed or even increased. This, however, is not a disadvantage,-

since in these zones the arch is already pretensioned to such an extent and is so slender that it is able to absorb the necessary deformation without danger.

Further features of the invention and details as regards the advantages attained will be seen from thefollowing detailed description in con- Fig. 3 is a similar section of another modifica tion of the wall with a bulged portion, and

Fig. 4 is a representation of a development of thewhole dam, on the line IVIV in Fig. 1.

Similar reference numerals denote similar parts in the different views;

Referring now to thedrawings in greater detail, and first to Fig.1, it will be'seen that the embodiment shown in this figure isa barrage by which a banked-up lake or water basin is to be formed between two opposite valley sides. The individual contours indicating the shape of the ground are denoted I.

In its'middle part under the action of the water pressure thedam has the shape of a segment of a circular cylinder having a vertical generating line. This part of the'dam is denoted 2 in Fig. 1. Numerals 3 and 4 designate the abutments which at both sides are joined to the cylindrical part '2 of the dam, and supported on foundation bases- 5, 6, arranged at the two sides, Fig. 4. The foundation bases 5 and. 6 arranged at the side are upwardlyinclined, as indicated in Fig. 4. By the composition of forces, i. e., the force produced under the action of the water pressure and the weight of the abutment, resultant forces are formed which act on the foundation base as far as possible in a vertical direction. The arrows shown in Fig. 4 indicate the directions on attack of these resultants.

The size of the angle of inclination of the foundation base can be calculated from the foregoing data; Where the calculated inclination of the foundation base is not existing in the natural ground, it must be artificially created by digging out. Since the horizontally directed forces are pressed downwards by the weight of theabutments Sand 4, the abutments are also given a form sloping-from-the crest M of thedam to th sides of the valley, as indicated'at l and 8 in Fig. 1.

Arrangedb'etween the abutments 3 and 4 and the'two sides'of-the'v'alley are secondary retaining'dams or walls 9 and Ill which in the illustrated embodiment are-curved as seen in plan owingto the conditions of the ground which have beenassumed in this case. retaining dams 9 and 10 are separated from the main dam by spacing joints so that they do not transmitany forces to the main dam.

The two secondaryv As will be seen from Fig. 2, the main dam 2 has a constant wall thickness throughout its height, and in its lower part joined to the foundation base it has a foot-like enlargement I l at its downstream side.

Arched dams so far used to be so designed that they had a considerably smaller wall thickness at the cap or crest of the dam than at other parts of the wall. As a rule, the walls were made with an increasing thickness towards the foundation.

Inregard to the stress caused by the water pressure the dam acts partly as a projection enclosedin-the' foundation and partly as an arch between-the abutments. An arch action can occur only as far as the dam is bent back in the direction of the water pressure, i. e., mainly in its upper parts. In its lower parts, on the other hand, the largest part of the water pressure must be transmitted to the'foundation by a cantilever action.

In a dam having a substantially'constant wall thickness from top to bottom, the conditions are more'favourable. Thecantilever effect cannot be so large since the wall thickness of the dam in the foundation base is small. The arch effect, on 'the' other hand, is somuch larger, since on the onehand the bending out under action of the cantilever moments is relatively large owing to the relatively small wall thickness of the dam, and on the other hand the arch force is relatively larger than in the conventional arch dams owingto the relatively large thickness of the daminits-upper part. Since the two measures, i. e., less wall thickness ,in the lower part and greater wall thicknessjin the upper part aim in thesame direction, i. e., towards an increase of the arch effect in relation to the cantilever effect, there is a surprisingly large conversion of the diagram of forces towards the arch effect. The increased arch effect is absolutely desirable, since in the design according to the invention the arch forces are transmitted to a foundation base rising in the sides of the valley while for taking the-thrusts in the bottom of th valley only a foundation base which in principle is horizontal will be available.

Fig. 3 shows-another modification of the cross section of the main dam which in this case is denoted 2'. This cross section in the example as per Fig. *3 is shaped so that above the foundation base'in the direction towards'the water side a reflex preliminary bulge I2 is produced which seats on the foundation base IS with an incline i3 directed towards the downstream'side of the dam.-

Fig. 4shows furtherdetails as regards the course of the cap .or crest M of the dam and the design of the foundation. base I5 of the main wall 2. The dotted line 16 illustrates the original shape of the ground in the region of the main dam 2 and the abutments 3 and 4.

As various embodiments of the invention are possible, and as various changes may be made in the embodiments above set forth, it is to be understood that all matter herein set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.-

Havin now particularly described and ascertained the nature. of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. An arch dam of concrete fora site flanked by hills, comprisinga main dam'having abutments inthe form of buttresses at both imposts of said arch founded on a base sloping up the hillsides, said dam also having two wing walls in the form of arched gravity dams, said buttresses, as viewed in plan, having their axes extending tangentially to said main wall, and said wing walls, as viewed in plan, having their axes extending at right angles to the axis of the main arch wall, foundations on said Wing walls, said foundations being slopingly received up the hillsides and anchored therein, said wing wall and said main wall being separated by spacing joints, and means for closing said joints.

2. An arch dam of the type claimed in claim 1, said dam having a curved main wall with the convex part of the curvature facing upstream, said wall having a sloping portion at the intersection thereof with the base.

ULRICH FINSTERWALDER.

REFERENCES CITED The following references are of record in the file of this patent:

OTHER REFERENCES Eng. News-Record, October 10, 1929, pp. 569-70. 

